1. Field of the Invention
This invention generally relates to document copying, scanning, and reproduction and, more particularly, to a system and method for correctly aligning a document during a digital document scanning process.
2. Description of the Related Art
As used herein, the term digital scanning, or scanning refers to copying, scanning, and document archiving using a digital process, especially using OCR technology. While scanning, it is often desirable to align the original document with the coordinate system of the scanner to reduce classification errors. Indeed, there are a variety of conventional scanners that employ various specialized apparatuses, such as automatic document feeders, guides, arms, etc., to physically align the original in order to avoid such problems.
However, it is not unusual for documents to be positioned manually on the scanner platen as well. This is especially true if the original is bound, e.g., a book or a journal. If the user is not careful in positioning the original or in closing the cover, the original may become misaligned relative to the scanning coordinate system. In the parlance of the industry, such rotational misalignment of a document is often referred to as skew.
FIG. 1 is a plan view of a document scanner and document coordinate systems (prior art). Note that the terms scanning coordinate system or scanner coordinate system refer to the 2-dimensional imaging coordinate system imposed on the digital image by the scanning process itself. Typically, one axis corresponds to the pixel readout along the scan bar (called x-axis for convenience). The other orthogonal axis corresponds to the direction of travel of the scan bar (called y-axis for convenience). The image of the original document has its own local coordinate system (for convenience referred to as the document coordinate system), which is defined relative to the scanner coordinate system.
As mentioned above, many scanners avoid the problem of skew altogether by employing special mechanisms like automatic document feeders, guides, or arms to physically align the document with the scanner coordinate system. However, the added processes reduce reliability and document throughput. Software solutions, on the other hand, rely on detecting the bounding contour of the document in order to determine the amount of skew. They frequently utilize special patterned or colored backings to facilitate the task of boundary detection, which can sometimes be “seen” through the paper being scanned. Generally, these solutions and manipulations add to the cost of the scanning system. Further, many software processes require extensive scanner device memory.
It would be advantageous if a scanned document could be deskewed without mechanical means, or without a specially patterned backing.
It would be advantageous if a scanned document could be deskewed with a simple and effective software process that minimized the use of memory.